Not for the first time, NAMA's Chief Executive Brendan McDonagh has lashed out at so-called land hoarders for exacerbating the housing crisis.

The agency sold plenty of land which can be used to build homes.

But many buyers are hoarding sites and happily watching their value spiral upwards instead of building badly needed homes, according to Mr McDonagh.

He says the agency sold land that could be used to build 50,000 homes but only 3,000 are under construction.

The Government's response to this concern is introducing a tax on vacant sites to reduce the incentive for land owners to hoard undeveloped land in areas zoned for housing.

The only problem is that the legislation is full of holes which will allow landowners wriggle out of paying.

At first glance, the vacant site levy looks credible.

The local authorities have published registers of vacant sites.

Dublin City Council's list is available here and it is remarkable how many vacant sites are owned by State bodies, including the local authority itself.

From January 2019, councils can impose a charge of 3% of the market value of vacant land if it is in an area in need of housing which is zoned for residential purposes.

However, there is an exemption if the land is in negative equity - in other words if the value of the loan exceeds the value of the site.

Therefore, many landowners can avoid paying by putting additional debt on the land.

This loophole has been highlighted by Social Democrat TD Róisín Shortall who has also called for the start date of 2019 to be brought forward in light of the urgent need for housing.

She has also suggested that the levy should rise the longer the site remains vacant.

Property sources say developers are sanguine about the vacant site levy because they can see how they can circumvent the charge.

But they argue landowners are not building apartments in areas such as Dublin city because the costs remain too high.

I found this hard to believe until a friend told me he had examined developing a site for apartments but was astonished by the costs and quickly abandoned the project.

Among them was the requirement in Dublin city to provide expensive underground car parking so each apartment has a space and VAT charge of 13.5%. There is no VAT in the UK.

Another factor is that the Government may have contributed to the problem of vacant sites itself.

In Budget 2012, then finance minister Michael Noonan granted a capital gains tax exemption for investors who bought prior to the end of December 2013 and held the property for seven years or more (this was later extended to the end of 2014.)

It was introduced at a time when Ireland was desperately trying to encourage investment in property to re-ignite the sector.

But it has created an incentive for landowners to retain sites even if they do not intend to use them.

The policy has the opposite effect of the vacant site levy which is designed to encourage landowners to sell it if they don't plan to build on land.

The Government should consider two steps to get construction under way to help solve the housing crisis.

Firstly, it should fix the loopholes in the vacant site levy which will be unpopular with developers.

Secondly, it should see if costs can be temporally reduced for the construction of apartments in areas of critical need.

That will appease developers and might get them moving.

The State is not going to be able to build all the homes needed to solve the crisis on its own.

It needs the private sector to do the heavy lifting.

Right now that does not seem to be happening.

Comments welcome via Twitter to @davidmurphyRTE